Umihara Kawase Gaiden

After a storm, Umihara Kawase and her friend, Kouichi Shioji, who were sailing on the high seas, ran aground on the coast of an island and discovered through a local resident that there is a treasure hidden at the bottom of the sea. During the storm, Kawase was hearing a sad voice singing a sad song, soon, they discover that the supposed treasure is being guarded by a huge Zeuglodon (Basilosaurus). Could this creature be related to the voice that Kawase hears coming from the sea?